At some point in humanity's future, our military forces are going to have to fight alien invaders, angry robots or hordes of zombies. Ultimately, a bunch of infantry grunts are going to have to hold the line against the onslaught. And they're going to need guns. Awesome guns. What have the arms merchants of the world been cooking up? Here are the five guns Popular Mechanics thinks are the most promising.XM-25 (pictured) - This grenade launcher has two things going for it: a laser range finder and shrapnel grenades with computer chips in them. What does this mean for soldiers? Imagine a bunch of aliens taking cover around a corner. Measure and set the range for just past the corner, fire a grenade, and watch as it completely negates their cover. This is basically a weapon you can't hide from. Corner Shot Launcher - This Israeli/German weapon is also intended to eliminate the advantage of cover by allowing a soldier to peer around a corner with a video camera and then fire a grenade or smaller round using the collapsible firing post that can bend up to 90 degrees. SCAR-Light - This rifle could be the replacement for the M-16, which was first introduced in 1964. It's basically a light, accurate, reliable gun with quick change barrels for different environments and easily replaceable parts. Sometimes simpler is better, although what's with the super creepy name? FMG9 Folding Machine Gun - I'm not sure the world really needs a submachine gun that folds into a brick small enough to fit in a large pocket, and switches instantly from "brick" to "blazing instrument of death" with the push of a button. Can we uninvent this, please? SAR 21 - This weapon is distinguished by the fact that the Singapore military has been using it for years. It's powerful and accurate, has integrated laser sights, is compact for fighting in tight quarters and is designed with a limited "straight back" recoil that doesn't affect accuracy. You have to wonder if the main reason the U.S. isn't using it is because it's made in Singapore. So, no ray guns, which is kind of disappointing, and a lot of money and brainpower is being spent on developing efficient killing tools, which is also pretty disappointing, since we all know none of these will probably ever be used against alien invaders or zombies. Image by ATK.Top 5 High-Tech Guns for Next-Gen Infantry. [Popular Mechanics]